This invention relates to solar heating systems and more particularly to a solar collector system which can be integrally incorporated in a building, such as a single or multi-family residence or commercial building, constructed in accordance with generally recognized building construction practices.
In view of the increasing concern of diminishing supplies and increasing costs of conventional energy forms, solar heating offers an attractive alternate method for heating residences and other types of buildings because of the general availability of solar energy and its non-polluting characteristics. Basically, solar heating systems involve collecting incident solar radiation, transferring this solar radiation into heat energy, and then utilizing this heat energy for heating a building. Here, we are particularly concerned with a non-concentrating immovable solar collector which uses air as the heat transfer medium. Solar collectors, such as above described, are usually installed on a stationary structure, such as on the roof of a house or other building, and are aligned in an optimum direction and at an optimum inclination for intercepting the largest possible percentage of solar radiation available at all times of the solar day and during all times of the heating season. These stationary solar collectors are much less expensive than are movable collectors.
Of course, at any given latitude and at any given time of the day and the year, only a given amount of solar radiation (or insolation as measured in BTU/ft.sup.2 hr) strikes the earth's surface. Unfortunately, at higher latitudes where the heating requirements are the highest, there is not only less available insolation in the winter months but the time available for each day for solar heating is descreased (i.e., there is less daylight) thus requiring larger area collectors. Since in most conventional solar heating systems the collectors are a major cost factor, it is highly desirable that the collectors be as efficient as possible so as to decrease their size and numbers required to heat the building.
The solar collector system of the present invention utilizes air as the heat transfer medium. In most prior forced air solar collector systems, solar radiation passes through a transparent panel and is absorbed within the collector by various solar radiation absorption surfaces, such as the walls of the collector or closely spaced cups or other means disposed within the collector. Air is then forced over the absorption surfaces within the collector and is heated by the absorption surfaces. The heated air is then circulated to a large heat sink, such as a large volume of water or crushed rock, where the heated air heats the sink. Air may then be circulated through the sink for being heated thereby and this newly heated air is then circulated through the building for heating purposes. Oftentimes, the heat sink will store sufficient heat to adequately heat the building for several days in the event cloudy weather blocks out solar radiation. Auxiliary heating units in the heating system are usually provided so that in the event solar radiation is not sufficient to heat the building, the auxiliary heaters can be used to augment solar heating.
As previously mentioned, it is highly desirable that a forced air solar collector be as efficient as possible in converting solar radiation into heat energy and in heating the air circulated therethrough. The overall efficiency of the solar collector may be expressed as the ratio of the heat added to the air circulated through the collector in a given period of time compared to the insolation available during that period in the plane of the collector surface. In order to maximize the efficiency of any solar collector, it is desirable that the temperature of the radiation absorption surfaces be as low as possible so as to reduce reradiation and conduction losses from the absorbing surface and thereby to insure that the maximum available amount of heat possible is transferred to the air circulated through the collector. It is also desirable that the ducting losses of the air circulated through the collector be as low as possible so as to reduce the energy required to circulate the air through the collector. It is generally known that in order to increase the transfer of heat to air that the air should be rapidly and turbulently circulated over the heated surfaces thereby to increase the heat transfer coefficient between the air and heated surfaces. This, however, requires a greater expenditure of energy to circulate the air.
Reference may be made to such U.S. Pat. Nos. as 2,680,565 and 3,971,359 which describe solar heating collectors broadly similar to this invention.